diff --git a/spec/unit/rendezvous/ecdhv1.spec.ts b/spec/unit/rendezvous/ecdhv1.spec.ts
new file mode 100644
index 000000000..f088977f0
--- /dev/null
+++ b/spec/unit/rendezvous/ecdhv1.spec.ts
@@ -0,0 +1,172 @@
+/*
+Copyright 2022 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import "../../olm-loader";
+import { RendezvousFailureReason, RendezvousIntent } from "../../../src/rendezvous";
+import { MSC3903ECDHPayload, MSC3903ECDHv1RendezvousChannel } from "../../../src/rendezvous/channels";
+import { decodeBase64 } from "../../../src/crypto/olmlib";
+import { DummyTransport } from "./DummyTransport";
+
+function makeTransport(name: string) {
+    return new DummyTransport<any, MSC3903ECDHPayload>(name, { type: "dummy" });
+}
+
+describe("ECDHv1", function () {
+    beforeAll(async function () {
+        await global.Olm.init();
+    });
+
+    describe("with crypto", () => {
+        it("initiator wants to sign in", async function () {
+            const aliceTransport = makeTransport("Alice");
+            const bobTransport = makeTransport("Bob");
+            aliceTransport.otherParty = bobTransport;
+            bobTransport.otherParty = aliceTransport;
+
+            // alice is signing in initiates and generates a code
+            const alice = new MSC3903ECDHv1RendezvousChannel(aliceTransport);
+            const aliceCode = await alice.generateCode(RendezvousIntent.LOGIN_ON_NEW_DEVICE);
+            const bob = new MSC3903ECDHv1RendezvousChannel(bobTransport, decodeBase64(aliceCode.rendezvous.key));
+
+            const bobChecksum = await bob.connect();
+            const aliceChecksum = await alice.connect();
+
+            expect(aliceChecksum).toEqual(bobChecksum);
+
+            const message = { key: "xxx" };
+            await alice.send(message);
+            const bobReceive = await bob.receive();
+            expect(bobReceive).toEqual(message);
+
+            await alice.cancel(RendezvousFailureReason.Unknown);
+            await bob.cancel(RendezvousFailureReason.Unknown);
+        });
+
+        it("initiator wants to reciprocate", async function () {
+            const aliceTransport = makeTransport("Alice");
+            const bobTransport = makeTransport("Bob");
+            aliceTransport.otherParty = bobTransport;
+            bobTransport.otherParty = aliceTransport;
+
+            // alice is signing in initiates and generates a code
+            const alice = new MSC3903ECDHv1RendezvousChannel(aliceTransport);
+            const aliceCode = await alice.generateCode(RendezvousIntent.LOGIN_ON_NEW_DEVICE);
+            const bob = new MSC3903ECDHv1RendezvousChannel(bobTransport, decodeBase64(aliceCode.rendezvous.key));
+
+            const bobChecksum = await bob.connect();
+            const aliceChecksum = await alice.connect();
+
+            expect(aliceChecksum).toEqual(bobChecksum);
+
+            const message = { key: "xxx" };
+            await bob.send(message);
+            const aliceReceive = await alice.receive();
+            expect(aliceReceive).toEqual(message);
+
+            await alice.cancel(RendezvousFailureReason.Unknown);
+            await bob.cancel(RendezvousFailureReason.Unknown);
+        });
+
+        it("double connect", async function () {
+            const aliceTransport = makeTransport("Alice");
+            const bobTransport = makeTransport("Bob");
+            aliceTransport.otherParty = bobTransport;
+            bobTransport.otherParty = aliceTransport;
+
+            // alice is signing in initiates and generates a code
+            const alice = new MSC3903ECDHv1RendezvousChannel(aliceTransport);
+            const aliceCode = await alice.generateCode(RendezvousIntent.LOGIN_ON_NEW_DEVICE);
+            const bob = new MSC3903ECDHv1RendezvousChannel(bobTransport, decodeBase64(aliceCode.rendezvous.key));
+
+            const bobChecksum = await bob.connect();
+            const aliceChecksum = await alice.connect();
+
+            expect(aliceChecksum).toEqual(bobChecksum);
+
+            expect(alice.connect()).rejects.toThrow();
+
+            await alice.cancel(RendezvousFailureReason.Unknown);
+            await bob.cancel(RendezvousFailureReason.Unknown);
+        });
+
+        it("closed", async function () {
+            const aliceTransport = makeTransport("Alice");
+            const bobTransport = makeTransport("Bob");
+            aliceTransport.otherParty = bobTransport;
+            bobTransport.otherParty = aliceTransport;
+
+            // alice is signing in initiates and generates a code
+            const alice = new MSC3903ECDHv1RendezvousChannel(aliceTransport);
+            const aliceCode = await alice.generateCode(RendezvousIntent.LOGIN_ON_NEW_DEVICE);
+            const bob = new MSC3903ECDHv1RendezvousChannel(bobTransport, decodeBase64(aliceCode.rendezvous.key));
+
+            const bobChecksum = await bob.connect();
+            const aliceChecksum = await alice.connect();
+
+            expect(aliceChecksum).toEqual(bobChecksum);
+
+            alice.close();
+
+            expect(alice.connect()).rejects.toThrow();
+            expect(alice.send({})).rejects.toThrow();
+            expect(alice.receive()).rejects.toThrow();
+
+            await alice.cancel(RendezvousFailureReason.Unknown);
+            await bob.cancel(RendezvousFailureReason.Unknown);
+        });
+
+        it("require ciphertext", async function () {
+            const aliceTransport = makeTransport("Alice");
+            const bobTransport = makeTransport("Bob");
+            aliceTransport.otherParty = bobTransport;
+            bobTransport.otherParty = aliceTransport;
+
+            // alice is signing in initiates and generates a code
+            const alice = new MSC3903ECDHv1RendezvousChannel(aliceTransport);
+            const aliceCode = await alice.generateCode(RendezvousIntent.LOGIN_ON_NEW_DEVICE);
+            const bob = new MSC3903ECDHv1RendezvousChannel(bobTransport, decodeBase64(aliceCode.rendezvous.key));
+
+            const bobChecksum = await bob.connect();
+            const aliceChecksum = await alice.connect();
+
+            expect(aliceChecksum).toEqual(bobChecksum);
+
+            // send a message without encryption
+            await aliceTransport.send({ iv: "dummy", ciphertext: "dummy" });
+            expect(bob.receive()).rejects.toThrow();
+
+            await alice.cancel(RendezvousFailureReason.Unknown);
+            await bob.cancel(RendezvousFailureReason.Unknown);
+        });
+
+        it("ciphertext before set up", async function () {
+            const aliceTransport = makeTransport("Alice");
+            const bobTransport = makeTransport("Bob");
+            aliceTransport.otherParty = bobTransport;
+            bobTransport.otherParty = aliceTransport;
+
+            // alice is signing in initiates and generates a code
+            const alice = new MSC3903ECDHv1RendezvousChannel(aliceTransport);
+            await alice.generateCode(RendezvousIntent.LOGIN_ON_NEW_DEVICE);
+
+            await bobTransport.send({ iv: "dummy", ciphertext: "dummy" });
+
+            expect(alice.receive()).rejects.toThrow();
+
+            await alice.cancel(RendezvousFailureReason.Unknown);
+        });
+    });
+});
diff --git a/spec/unit/rendezvous/ecdh.spec.ts b/spec/unit/rendezvous/ecdhv2.spec.ts
similarity index 100%
rename from spec/unit/rendezvous/ecdh.spec.ts
rename to spec/unit/rendezvous/ecdhv2.spec.ts
diff --git a/src/rendezvous/channels/MSC3903ECDHv1RendezvousChannel.ts b/src/rendezvous/channels/MSC3903ECDHv1RendezvousChannel.ts
new file mode 100644
index 000000000..573ae6f22
--- /dev/null
+++ b/src/rendezvous/channels/MSC3903ECDHv1RendezvousChannel.ts
@@ -0,0 +1,256 @@
+/*
+Copyright 2022 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { SAS } from "@matrix-org/olm";
+
+import {
+    RendezvousError,
+    RendezvousCode,
+    RendezvousIntent,
+    RendezvousChannel,
+    RendezvousTransportDetails,
+    RendezvousTransport,
+    RendezvousFailureReason,
+} from "..";
+import { encodeBase64, decodeBase64 } from "../../crypto/olmlib";
+import { crypto, subtleCrypto, TextEncoder } from "../../crypto/crypto";
+import { generateDecimalSas } from "../../crypto/verification/SASDecimal";
+import { UnstableValue } from "../../NamespacedValue";
+import { EncryptedPayload, MSC3903ECDHPayload, PlainTextPayload } from "./MSC3903ECDHv2RendezvousChannel";
+
+/**
+ * @deprecated Use ECDH_V2 instead
+ */
+export const ECDH_V1 = new UnstableValue(
+    "m.rendezvous.v1.curve25519-aes-sha256",
+    "org.matrix.msc3903.rendezvous.v1.curve25519-aes-sha256",
+);
+
+/**
+ * @deprecated Use ECDHv2RendezvousCode instead
+ */
+export interface ECDHv1RendezvousCode extends RendezvousCode {
+    rendezvous: {
+        transport: RendezvousTransportDetails;
+        algorithm: typeof ECDH_V1.name | typeof ECDH_V1.altName;
+        key: string;
+    };
+}
+
+async function importKey(key: Uint8Array): Promise<CryptoKey> {
+    if (!subtleCrypto) {
+        throw new Error("Web Crypto is not available");
+    }
+
+    const imported = subtleCrypto.importKey("raw", key, { name: "AES-GCM" }, false, ["encrypt", "decrypt"]);
+
+    return imported;
+}
+
+/**
+ * Implementation of the unstable [MSC3903](https://github.com/matrix-org/matrix-spec-proposals/pull/3903)
+ * X25519/ECDH key agreement based secure rendezvous channel.
+ * Note that this is UNSTABLE and may have breaking changes without notice.
+ *
+ * @deprecated Use MSC3903ECDHv2RendezvousChannel instead. This implementation will be removed.
+ */
+export class MSC3903ECDHv1RendezvousChannel<T> implements RendezvousChannel<T> {
+    private olmSAS?: SAS;
+    private ourPublicKey: Uint8Array;
+    private aesKey?: CryptoKey;
+    private connected = false;
+
+    public constructor(
+        private transport: RendezvousTransport<MSC3903ECDHPayload>,
+        private theirPublicKey?: Uint8Array,
+        public onFailure?: (reason: RendezvousFailureReason) => void,
+    ) {
+        this.olmSAS = new global.Olm.SAS();
+        this.ourPublicKey = decodeBase64(this.olmSAS.get_pubkey());
+    }
+
+    public async generateCode(intent: RendezvousIntent): Promise<ECDHv1RendezvousCode> {
+        if (this.transport.ready) {
+            throw new Error("Code already generated");
+        }
+
+        await this.transport.send({ algorithm: ECDH_V1.name });
+
+        const rendezvous: ECDHv1RendezvousCode = {
+            rendezvous: {
+                algorithm: ECDH_V1.name,
+                key: encodeBase64(this.ourPublicKey),
+                transport: await this.transport.details(),
+            },
+            intent,
+        };
+
+        return rendezvous;
+    }
+
+    public async connect(): Promise<string> {
+        if (this.connected) {
+            throw new Error("Channel already connected");
+        }
+
+        if (!this.olmSAS) {
+            throw new Error("Channel closed");
+        }
+
+        const isInitiator = !this.theirPublicKey;
+
+        if (isInitiator) {
+            // wait for the other side to send us their public key
+            const rawRes = await this.transport.receive();
+            if (!rawRes) {
+                throw new Error("No response from other device");
+            }
+            const res = rawRes as Partial<PlainTextPayload>;
+            const { key, algorithm } = res;
+            if (!algorithm || !ECDH_V1.matches(algorithm) || !key) {
+                throw new RendezvousError(
+                    "Unsupported algorithm: " + algorithm,
+                    RendezvousFailureReason.UnsupportedAlgorithm,
+                );
+            }
+
+            this.theirPublicKey = decodeBase64(key);
+        } else {
+            // send our public key unencrypted
+            await this.transport.send({
+                algorithm: ECDH_V1.name,
+                key: encodeBase64(this.ourPublicKey),
+            });
+        }
+
+        this.connected = true;
+
+        this.olmSAS.set_their_key(encodeBase64(this.theirPublicKey!));
+
+        const initiatorKey = isInitiator ? this.ourPublicKey : this.theirPublicKey!;
+        const recipientKey = isInitiator ? this.theirPublicKey! : this.ourPublicKey;
+        let aesInfo = ECDH_V1.name;
+        aesInfo += `|${encodeBase64(initiatorKey)}`;
+        aesInfo += `|${encodeBase64(recipientKey)}`;
+
+        const aesKeyBytes = this.olmSAS.generate_bytes(aesInfo, 32);
+
+        this.aesKey = await importKey(aesKeyBytes);
+
+        // blank the bytes out to make sure not kept in memory
+        aesKeyBytes.fill(0);
+
+        const rawChecksum = this.olmSAS.generate_bytes(aesInfo, 5);
+        return generateDecimalSas(Array.from(rawChecksum)).join("-");
+    }
+
+    private async encrypt(data: T): Promise<MSC3903ECDHPayload> {
+        if (!subtleCrypto) {
+            throw new Error("Web Crypto is not available");
+        }
+
+        const iv = new Uint8Array(32);
+        crypto.getRandomValues(iv);
+
+        const encodedData = new TextEncoder().encode(JSON.stringify(data));
+
+        const ciphertext = await subtleCrypto.encrypt(
+            {
+                name: "AES-GCM",
+                iv,
+                tagLength: 128,
+            },
+            this.aesKey as CryptoKey,
+            encodedData,
+        );
+
+        return {
+            iv: encodeBase64(iv),
+            ciphertext: encodeBase64(ciphertext),
+        };
+    }
+
+    public async send(payload: T): Promise<void> {
+        if (!this.olmSAS) {
+            throw new Error("Channel closed");
+        }
+
+        if (!this.aesKey) {
+            throw new Error("Shared secret not set up");
+        }
+
+        return this.transport.send(await this.encrypt(payload));
+    }
+
+    private async decrypt({ iv, ciphertext }: EncryptedPayload): Promise<Partial<T>> {
+        if (!ciphertext || !iv) {
+            throw new Error("Missing ciphertext and/or iv");
+        }
+
+        const ciphertextBytes = decodeBase64(ciphertext);
+
+        if (!subtleCrypto) {
+            throw new Error("Web Crypto is not available");
+        }
+
+        const plaintext = await subtleCrypto.decrypt(
+            {
+                name: "AES-GCM",
+                iv: decodeBase64(iv),
+                tagLength: 128,
+            },
+            this.aesKey as CryptoKey,
+            ciphertextBytes,
+        );
+
+        return JSON.parse(new TextDecoder().decode(new Uint8Array(plaintext)));
+    }
+
+    public async receive(): Promise<Partial<T> | undefined> {
+        if (!this.olmSAS) {
+            throw new Error("Channel closed");
+        }
+        if (!this.aesKey) {
+            throw new Error("Shared secret not set up");
+        }
+
+        const rawData = await this.transport.receive();
+        if (!rawData) {
+            return undefined;
+        }
+        const data = rawData as Partial<EncryptedPayload>;
+        if (data.ciphertext && data.iv) {
+            return this.decrypt(data as EncryptedPayload);
+        }
+
+        throw new Error("Data received but no ciphertext");
+    }
+
+    public async close(): Promise<void> {
+        if (this.olmSAS) {
+            this.olmSAS.free();
+            this.olmSAS = undefined;
+        }
+    }
+
+    public async cancel(reason: RendezvousFailureReason): Promise<void> {
+        try {
+            await this.transport.cancel(reason);
+        } finally {
+            await this.close();
+        }
+    }
+}
diff --git a/src/rendezvous/channels/MSC3903ECDHv2RendezvousChannel.ts b/src/rendezvous/channels/MSC3903ECDHv2RendezvousChannel.ts
index cd1ac47be..312aaa5c2 100644
--- a/src/rendezvous/channels/MSC3903ECDHv2RendezvousChannel.ts
+++ b/src/rendezvous/channels/MSC3903ECDHv2RendezvousChannel.ts
@@ -29,8 +29,9 @@ import { encodeUnpaddedBase64, decodeBase64 } from "../../crypto/olmlib";
 import { crypto, subtleCrypto, TextEncoder } from "../../crypto/crypto";
 import { generateDecimalSas } from "../../crypto/verification/SASDecimal";
 import { UnstableValue } from "../../NamespacedValue";
+import { ECDH_V1 } from "./MSC3903ECDHv1RendezvousChannel";
 
-const ECDH = new UnstableValue(
+const ECDH_V2 = new UnstableValue(
     "m.rendezvous.v2.curve25519-aes-sha256",
     "org.matrix.msc3903.rendezvous.v2.curve25519-aes-sha256",
 );
@@ -38,7 +39,7 @@ const ECDH = new UnstableValue(
 export interface ECDHv2RendezvousCode extends RendezvousCode {
     rendezvous: {
         transport: RendezvousTransportDetails;
-        algorithm: typeof ECDH.name | typeof ECDH.altName;
+        algorithm: typeof ECDH_V2.name | typeof ECDH_V2.altName | typeof ECDH_V1.name | typeof ECDH_V1.altName;
         key: string;
     };
 }
@@ -46,7 +47,7 @@ export interface ECDHv2RendezvousCode extends RendezvousCode {
 export type MSC3903ECDHPayload = PlainTextPayload | EncryptedPayload;
 
 export interface PlainTextPayload {
-    algorithm: typeof ECDH.name | typeof ECDH.altName;
+    algorithm: typeof ECDH_V2.name | typeof ECDH_V2.altName | typeof ECDH_V1.name | typeof ECDH_V1.altName;
     key?: string;
 }
 
@@ -90,11 +91,11 @@ export class MSC3903ECDHv2RendezvousChannel<T> implements RendezvousChannel<T> {
             throw new Error("Code already generated");
         }
 
-        await this.transport.send({ algorithm: ECDH.name });
+        await this.transport.send({ algorithm: ECDH_V2.name });
 
         const rendezvous: ECDHv2RendezvousCode = {
             rendezvous: {
-                algorithm: ECDH.name,
+                algorithm: ECDH_V2.name,
                 key: encodeUnpaddedBase64(this.ourPublicKey),
                 transport: await this.transport.details(),
             },
@@ -123,7 +124,7 @@ export class MSC3903ECDHv2RendezvousChannel<T> implements RendezvousChannel<T> {
             }
             const res = rawRes as Partial<PlainTextPayload>;
             const { key, algorithm } = res;
-            if (!algorithm || !ECDH.matches(algorithm) || !key) {
+            if (!algorithm || !ECDH_V2.matches(algorithm) || !key) {
                 throw new RendezvousError(
                     "Unsupported algorithm: " + algorithm,
                     RendezvousFailureReason.UnsupportedAlgorithm,
@@ -134,7 +135,7 @@ export class MSC3903ECDHv2RendezvousChannel<T> implements RendezvousChannel<T> {
         } else {
             // send our public key unencrypted
             await this.transport.send({
-                algorithm: ECDH.name,
+                algorithm: ECDH_V2.name,
                 key: encodeUnpaddedBase64(this.ourPublicKey),
             });
         }
@@ -145,7 +146,7 @@ export class MSC3903ECDHv2RendezvousChannel<T> implements RendezvousChannel<T> {
 
         const initiatorKey = isInitiator ? this.ourPublicKey : this.theirPublicKey!;
         const recipientKey = isInitiator ? this.theirPublicKey! : this.ourPublicKey;
-        let aesInfo = ECDH.name;
+        let aesInfo = ECDH_V2.name;
         aesInfo += `|${encodeUnpaddedBase64(initiatorKey)}`;
         aesInfo += `|${encodeUnpaddedBase64(recipientKey)}`;
 
diff --git a/src/rendezvous/channels/index.ts b/src/rendezvous/channels/index.ts
index f157bbeae..42e0ee15e 100644
--- a/src/rendezvous/channels/index.ts
+++ b/src/rendezvous/channels/index.ts
@@ -14,4 +14,5 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+export * from "./MSC3903ECDHv1RendezvousChannel";
 export * from "./MSC3903ECDHv2RendezvousChannel";